Radio antenna



FIG. 1 is a perspective view from above the radio antenna;

FIG. 2 is a side view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof; and,

FIG. 5 is a side view thereof, showing placement.

The broken lines in the figures depict portions of the radio antenna and environment that form no part of the claimed design. 

CLAIM The ornamental design for a radio antenna, substantially as shown and described. 